There are many applications where a person requires supplemental oxygen to assist in effective respiration when breathing. Some examples include mining, fire fighting, diving, working in dangerous atmospheres, and flying in small non-pressurized aircraft. In high altitude environments the oxygen available for respiration in ambient air is depleted and supplemental oxygen is also required.
In many of these situations, oxygen is delivered at a steady flow rate and much of the delivered oxygen is wasted. This is because a person needs oxygen available only during the inspiratory phase of their respiratory cycle. Also, most of the oxygen systems used for such applications are heavy and cumbersome, not very portable, and depending on the system used, the oxygen supply may last for only relatively short periods of time.
Patients suffering from certain advanced stages of chronic obstructive pulmonary disease (COPD) are often treated by the administration of long term supplemental oxygen therapy. Common COPD's include pulmonary emphysema, chronic bronchitis, and severe asthma.
Devices which are commonly used to deliver oxygen to a person meter the oxygen at a fixed flow rate and thereby deliver a constant stream of oxygen. The oxygen is received by the person usually through an oxygen mask placed over the nose and mouth, or by nasal oxygen cannula inserted into the external nares of a person's nostrils. An oxygen catheter may sometimes be used to deliver oxygen for transtracheal oxygen therapy.
When breathing, a person inhales and exhales during each respiratory cycle. The inhalation or inspiratory phase is usually of much shorter duration than the exhalation or expiratory phase. This is termed the "I/E Ratio" and is approximately 1:2. There is also a pause at the end of each expiratory phase just prior to inhaling. When oxygen is administered at a steady flow to a person throughout their entire respiratory cycle, it is totally wasted during the exhalation phase, and during this pause. It is also wasted during the latter portion of the inspiratory phase (approximately 50%-60%) due to deadspace ventilation.
As medical oxygen is an anhydrous gas, water must be added with an attached humidifying device when using steady flow rate systems. This is particularly true for long term oxygen therapy. If oxygen is delivered during the first part of the inspiratory phase, a humidifier, with its potential problems of contamination by infection, is not needed.
Devices have been developed to conserve oxygen by intermittently regulating the oxygen flow in response to the inhalation stage of the respiratory cycle. Typical of such devices are those of Myers, U.S. Pat. No. 4,054,133, and Mon, U.S. Pat. No. 4,381,002. Each of these patents disclose devices which sense inhalation and exhalation pressures in the nasal cavity of a patient and convert those sensed pressure differentials to signals which control the flow of oxygen to a patient. Typically, oxygen flow is started upon the sensing of a negative pressure relative to atmospheric indicating the start of an inspiration period. Oxygen flow is then stopped at a second signal produced by the sensing of a positive pressure relative to atmospheric indicating the start of the expiration period.
Sato et al., in U.S. Pat. No. 4,681,099 disclose a non-portable breath-synchronized concentrated oxygen supplier comprising an air compressor, two absorption cylinders, a reservoir tank, an oxygen concentrator for producing and storing oxygen-enriched gas, a buffer tank having an inlet connected to the oxygen concentrator and an outlet for temporarily storing the oxygen enriched gas obtained from the concentrator.
Sato et al. disclose a thermocouple 28 which is used in the nose connecting cannula of the oxygen supplier and is used to directly sense the inspiration and exhalation of the respiration cycle of the patient. The thermocouple generates an output signal indicative of the inhalation and exhalation stages of the respiration. The thermocouple 28 is electrical current intensive and draws a continuous current from the electrical power supply according to a sinusoidal pattern as illustrated in FIG. 4A (column 10, lines 50 to 57). This continuous current draw necessitates large power requirements. Sato et al. also disclose a breath synchronizing solenoid valve 24 which is controlled by a gas regulator 29. The regulator 29 electrically opens the solenoid valve 24 at the beginning of each inhalation phase and maintains the solenoid valve in an open position for a length of time by delivering a continuous electrical current to the solenoid valve 24. The open time is based on a period determined by a combination of averaging the preceding inhalation durations in the ratio set on an input device. A continuous flow of electrical current is required in order to maintain the solenoid valve 24 in an open position during the majority of each inhalation phase as demonstrated in FIG. 4B. The breath-synchronized concentrated oxygen supplier disclosed by Sato et al. is not suitable for portable use because it continuously consumes substantial amounts of electrical power which quickly drains a battery system. No teaching or suggestion of conserving electrical power consumption is demonstrated in Sato et al.
The Puritan-Bennett 7200 Series respirators are complex, expensive, non-portable systems. The 7200 Series respirators require hook-up to a constant source of electrical current, typically a wall plug or the like. Further, while the Puritan-Bennett 7200 Series Respirators disclose a number of sensors, and sophisticated programming which can be manually manipulated to correspond with breathing cycles of specific patients, including assisting in respiration of a patient, there is no disclosure in the 7200 Series brochures which teaches the applicant's unique concept of prolonging the life of a portable battery, and the oxygen delivering respiratory gas system, by minimizing electricity consumption. This is done by drawing the electrical current in two brief pulses, coordinated respectively with the onset and termination of the inspiration phase of the patient. As explained above, this feature vastly prolongs the life of the applicant's unique apparatus. Since the Puritan-Bennett 7200 Series respirators are connected to permanent sources of power supply, the concepts of portability, and minimizing battery current demand, do not arise.
It is noted that even if the teachings of Sato et al. and Puritan-Bennett 7200 Series are combined, a possibility, incidentally, which is not taught in either citation, one still does not arrive at the applicant's unique portable respiratory system. One still would not devise a portable oxygen supply system which delivered brief pulses of electrical current at the beginning and the end of inspiration of a patient.
Durkan, in U.S. Pat. No. 4,457,303, describes a respirator system which uses a fluidic laminar proportional amplifier to sense the start of an inspiration period. Oxygen flow to a patient is immediately started in response to the sensed inspiration. Timing means, also started in response to the sensed inspiration, stops the oxygen flow after a preset period of time which is shorter than the inspiration period. As a result, oxygen is supplied to a patient only during the effective early stages of an inspiration resulting in an oxygen savings of as much as 70 percent as compared to a continuous flow administration.
Perkins, in U.S. Pat. No. 4,705,034, Nov. 10, 1987, U.S. Pat. No. 4,873,971, Oct. 17, 1989 and U.S. Pat. No. 5,005,570, Apr. 9, 1991, discloses a device for administering oxygen and other respirating gases to a patient which premeters and temporarily stores single does quantities of respirating gas and dispenses each dose in synchronization with the patient's inspiratory cycle. A sensor produces a signal upon the onset of each inhalation and a single dose of gas is dispensed to the patient in immediate response to the sensor signal.
Smith et al., U.S. Pat. No. 4,823,788, Apr. 25, 1989, disclose a method and apparatus for computer controlling the flow of breathing gas such as oxygen through a cannula or "mask" to a person by limiting gas delivery to the inhalation part of the breathing cycle. A bidirectional dynamic mass flow sensor senses the rate of flow of a gas through it and yields an output voltage proportional to mass flow and direction of gas movement. The measured dynamic flow signal is applied to a system computer controller which operates a flow controller. The system computer controller provides for indications of operation such as system failure and apnea, rate of flow, duration of flow, and total consumption. In addition, computer controls are provided to set the duration of gas flow in each breathing cycle.
Perkins, in U.S. Pat. No. 4,932,401, Jun. 12, 1990, discloses a displacement metering device for administering a mixture of oxygen and an anaesthetic gas to a patient, which measures single dose quantities of each of the two gases in separate sets of gas displacing means and dispenses a dose of each gas in admixture to a patient during the inspiration phase of the patient's respiratory cycle. Coordinating means ensure that the two gases are delivered in constant ratio and also provide means for changing the ratio between the two gases. Means are also provided to change the volume or dose size, of the two administered gases.
None of these devices disclose a means for measuring total oxygen consumed by the person so that this quantity can be accurately measured. There is therefore no way that health authorities and social medicine regulatory bodies which operate medical assistance programs, can monitor the amount of oxygen consumed and hence prevent fraudulent claims of oxygen consumption to be policed.
None of these patents disclose an oxygen controller and respiratory monitor which has a liquid crystal display face which on command will display a wide variety of information about the person consuming the oxygen, the condition of the monitor, and other critical parameters.
None of these references demonstrate an oxygen controller and respiratory monitor which by conserving the consumption of electricity, is readily portable and self-sustaining for long periods of time and can be connected to a personal computer-printer.